Rf-electrode surface and method of fabrication

ABSTRACT

A system for applying radiofrequency energy to tissue comprising a probe, an energy-delivery surface, and an energy source. The energy-delivery surface is elastomeric with an electrically conductive knit component. The energy-delivery surface can be expanded within an interior of a patient&#39;s body to engage tissue and energy delivered from the source through the expanded surface.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/410,764 (Attorney Docket No. 37644-707.101) filed on Nov. 5, 2010,the contents of which is incorporated herein by reference.

This application is related to Ser. No. 12/541,043 (Attorney Docket No.027980-000110US) filed on Aug. 13, 2009 and to Ser. No. 12/541,050(Attorney Docket No. 027980-000120US) filed on Aug. 13, 2009, both ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electrosurgical devices and relatedmethods for rapid, controlled ablation of tissue. More particularly, thepresent invention relates to treating tissue with a radiofrequencycurrent delivered through an electrically non-conductive gas which isionized to capacitively couple to surrounding tissue through a thindielectric layer surrounding the gas.

The treatment of diseased organs, such as the uterus and thegallbladder, by ablation of an endometrial or mucosal layer surroundingthe interior of the organ has long been proposed. Such internal surfaceablation can be achieved by heating the surface, treating the surfacewith microwave energy, treating the surface with cryoablation, anddelivering radiofrequency energy to the surface. Of particular interestto the present invention, a variety of radiofrequency ablationstructures have been proposed including solid electrodes, balloonelectrodes, metalized fabric electrodes, and the like. While ofteneffective, at least most of the prior electrode designs have sufferedfrom one or more deficiencies, such as relatively slow treatment times,incomplete treatments, non-uniform ablation depths, and risk of injuryto adjacent organs.

For these reasons, it would be desirable to provide methods andapparatus for the radiofrequency ablation of internal tissue surfaceswhich are rapid, provide for uniform ablation depths, which assurecomplete ablation over the entire targeted surface, and which reduce therisk of injury to adjacent organs. At least some of these objectiveswill be met by the inventions described hereinbelow.

2. Description of the Background Art

U.S. Pat. No. 4,979,948, describes a balloon filled with an electrolytesolution for distributing radiofrequency current to a mucosal layer viacapacitive coupling. US 2008/097425, having common inventorship with thepresent application, describes delivering a pressurized flow of a liquidmedium which carries a radiofrequency current to tissue, where theliquid is ignited into a plasma as it passes through flow orifices. U.S.Pat. No. 5,891,134 describes a radiofrequency heater within an enclosedballoon. U.S. Pat. No. 6,041,260 describes radiofrequency electrodesdistributed over the exterior surface of a balloon which is inflated ina body cavity to be treated. U.S. Pat. No. 7,371,231 and US 2009/054892describe a conductive balloon having an exterior surface which acts asan electrode for performing endometrial ablation. U.S. Pat. No.5,191,883 describes bipolar heating of a medium within a balloon forthermal ablation. U.S. Pat. No. 6,736,811 and U.S. Pat. No. 5,925,038show an inflatable conductive electrode.

BRIEF SUMMARY OF THE INVENTION

The present invention provides methods, apparatus, and systems fortreating tissue of a patient. The treatment generally comprisesdelivering a radiofrequency current to the tissue in order to heat andusually ablate the tissue to a desired depth. Current is delivered tothe tissue from a radiofrequency energy source through a firstdielectric medium and a second dielectric medium in series with thefirst medium. The first dielectric medium will usually comprise anelectrically non-conductive gas which may be ionized to form a plasma,typically by application of a high voltage radiofrequency voltage, butoptionally by the direct application of heat to the gas, furtheroptionally by the application of both the high radiofrequency voltageand heat to the gas. The second dielectric medium will separate thefirst medium from the target tissue, typically comprising a thindielectric material, such as silicone or a silicone-based material, moretypically comprising a thin dielectric wall which defines an interiorchamber which contains the electrically non-conductive gas. Theradiofrequency current is thus delivered to the tissue by applying aradiofrequency voltage across the first and second dielectric media sothat the first dielectric becomes ionized, typically forming a gasplasma, and the second dielectric allows current flow to the tissue viacapacitive coupling.

Methods for treating tissue of a patient in accordance with the presentinvention comprise containing an electrically non-conductive gas in aninterior chamber of an applicator having a thin dielectric wallsurrounding at least a portion of the interior chamber. An externalsurface of the thin dielectric wall is engaged against a target regionof the tissue, and a radiofrequency voltage is applied across the gasand thin wall, where the voltage is sufficient to ionize the gas toinitiate a plasma in the gas and to capacitively couple the current inthe gas plasma across the dielectric wall and into the engaged tissue.

The electrically non-conductive gas may be held statically within thechamber, but will more often be actively flowing through the chamber ofthe applicator. The flow rate of the non-conductive gas will typicallybe in the range from about 1 ml/sec to 50 ml/sec, preferably from 10ml/sec to 30 ml/sec. The interior chamber will have a volume in therange from 0.01 ml to 100 ml, typically from 2 ml to 10 ml. Usually, theelectrically non-conductive gas will be argon or another noble gas ormixture of noble gases.

The dielectric wall of the applicator may assume a variety ofconfigurations. In a first embodiment, the dielectric wall will have agenerally fixed shape that will remain constant regardless of theinternal pressurization of the contained gas. Alternatively, thedielectric wall may be elastic, conformable, slack, or otherwise havinga changeable shape which can conform to the engaged tissue surface. Insome examples, the thin dielectric wall will comprise a balloon or otherinflatable structure which is expanded by increasing an internalpressure of the electrically non-conductive gas or other medium.Alternatively, a separate frame, cage, spring, or other mechanicaldeployment structure could be provided within an elastic or non-elasticconformable thin dielectric wall. In the latter case, the frame or otherstructure can be configured and reconfigured to shape the thindielectric wall as desired in the method.

The voltage is applied to the tissue by providing a first electrodesurface coupled to the non-conductive gas and a second electrode surfacecoupled to the patient tissue. A radiofrequency voltage is then appliedacross the first and second electrodes in order to both ionize theelectrically non-conductive gas (forming a plasma) within the interiorchamber and to capacitively couple the charged plasma with tissue acrossthe thin dielectric wall.

The voltage applied to the first and second dielectric media will dependon the distance between the first electrode surface and the dielectricwall as well as the resistance between the dielectric wall and thesecond electrode which is in contact with the tissue, typically being inthe range between 500V (rms) and 2500V (rms). In the exemplaryembodiments, the first electrode surface will usually be in or on theinterior chamber or a gas flow path leading to the interior chamber, andthe second electrode surface will be in contact with the patient'stissue, often being disposed on a shaft or other external surface of thetreatment device.

In a second aspect of the present invention, apparatus for deliveringradiofrequency current to tissue comprises a body having a support end,a working end, and an interior chamber. A thin dielectric wall surroundsat least a portion of the interior chamber and has an external surfacedisposed at the working end of the body. A gas inlet will be provided toconnect to the chamber for delivery of an electrically non-conductivegas, either in a continuously flowing mode or in a static mode. A firstelectrode structure is provided which has a surface exposed to eitherthe interior chamber or the gas inlet. A second electrode structure isalso provided and has a surface adapted to contact tissue, typicallybeing somewhere on the body, more typically being on a handle or shaftportion of the device. The apparatus further includes a radiofrequencypower supply connected to apply a radiofrequency voltage across thefirst and second electrode structures, wherein the voltage is sufficientto initiate ionization of the gas into a plasma within the chamber. Thevoltage will further be sufficient to capacitively couple the current inthe plasma across the dielectric wall and into tissue adjacent theexternal surface.

The specific structure of the body may vary. In a first example, thedielectric wall may comprise a rigid material, typically selected fromthe group consisting of a ceramic, glass, and polymer. The rigidmaterial may be formed into a variety of geometries, including a tube,sphere, or the like. Usually, the dielectric wall will have a thicknessin the range from about 0.002 in to 0.1 in, usually from 0.005 in to0.05 in.

In alternative embodiments, the dielectric wall may comprise aconformable material, typically a silicone. Such conformable dielectricwalls will typically have a thickness in the range from about 0.004 into 0.03 in, usually from 0.008 in to 0.015 in. The conformable wall maybe non-distensible or may be elastic so that the wall structure may beinflated. For either non-distensible or elastic dielectric walls, thedevice may further comprise a frame which supports the conformablematerial, usually where the frame can be expanded and contracted to openand close the dielectric wall.

The apparatus of the present invention will typically also include ashaft or other handle structure connected to the support end of thebody. Usually, the shaft will have a lumen which extends into the gasinlet of the body to deliver the electrically non-conductive gas to thechamber. The shaft or handle may also include at least a second lumenfor removing the electrically non-conductive gas from the chamber sothat the gas may be recirculated in a continuous flow. Often, the firstelectrode will be at least partly in the first lumen of the device,although it may also be within the chamber or within both the firstlumen and the chamber. The second electrode will usually be disposed atleast partly over an exterior surface of the device, typically over theshaft, although in certain systems the second electrode could bedisposed on a separate dispersal pod.

Apparatus according to the present invention will have an interiorchamber volume in the range from 0.01 ml to 20 ml, typically from 1 mlto 10 ml. The dielectric wall will have an area in the range from 1 mm²to 100 mm², typically from 5 mm² to 50 mm². The first electrode surfacewill have an area in contact with the electrically non-conductive gas inthe range from 0.01 mm² to 10 mm², typically from 1 mm² to 5 mm².Additionally, the second electrode structure will have an area availableto contact tissue in the range from 0.5 mm² to 50 mm², usually from 1mm² to 10 mm².

The radiofrequency power supply may be of general construction as oftenused in electrosurgery. The power supply will typically be configured todeliver a voltage in the range from 500 V (rms) to 2500 V (rms), usuallyfrom 600 V (rms) to 1200V (rms), typically at a current in the rangefrom 0.1 A to 1 A, typically from 0.2 A to 0.5 A, and at a frequency inthe range from 450 kHz to 550 MHz, usually from 480 kHz to 500 MHz.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the invention and to see how it may becarried out in practice, some preferred embodiments are next described,by way of non-limiting examples only, with reference to the accompanyingdrawings, in which like reference characters denote correspondingfeatures consistently throughout similar embodiments in the attacheddrawings.

FIG. 1 is a schematic view of an ablation system corresponding to theinvention, including an electrosurgical ablation probe, RF power sourceand controller.

FIG. 2A is a view of the ablation probe of FIG. 1 configured with asharp tip for ablation of a tumor.

FIG. 2B is another view of the probe of FIG. 2A after being penetratedinto the tumor.

FIG. 3 is an enlarged schematic view of the working end of the probe ofFIG. 1 that provides a gas electrode within an interior of a thin-walldielectric structure.

FIG. 4A is a sectional view of an alternative thin-wall cylindricaldielectric structure in which support elements are formed within thedielectric structure.

FIG. 4B is a sectional view of a portion of another thin-wall planardielectric structure in which support elements are in a waffle-likeconfiguration.

FIG. 5A is a sectional view of a portion of another thin-wall planardielectric structure in which support elements comprise post-likeelements.

FIG. 5B is a sectional view of a probe working end in which a thin-walldielectric structure with post-like support elements are provided aroundcore electrode.

FIG. 6 is a block diagram of components of one an electrosurgical systemcorresponding to the invention.

FIG. 7 is a block diagram of gas flow components of an electrosurgicalsystem corresponding to the invention.

FIG. 8 is a cut-away schematic view of a working end as in FIG. 3illustrating a step in a method of the invention wherein current iscoupled to tissue via a spark gap (or gas electrode) and capacitivecoupling through a thin-wall dielectric structure.

FIG. 9A is an enlarged schematic view of an aspect of the method of FIG.3 illustrating the step positioning an ionized gas electrode andthin-wall dielectric in contact with tissue.

FIG. 9B is a schematic view of a subsequent step of applying RF energyto create an arc across a gas and capacitive coupling through thethin-wall dielectric to cause current flow in a discrete path in tissue.

FIG. 9C is a schematic view similar to FIG. 9B depicting the scanning ofcurrent flow to another random path in the tissue.

FIG. 9D is a schematic view similar to FIGS. 9A-9C depicting the thermaldiffusion from the plurality of scanned current flows in the tissue.

FIG. 10 is a circuit diagram showing the electrical aspects andcomponents of the energy delivery modality.

FIG. 11A is a sectional view of the working end of FIG. 3 positioned intissue illustrating a step in a method of using the working end whereincurrent is coupled to tissue via an ionized gas and capacitive couplingthrough a thin wall dielectric structure.

FIG. 11B is a sectional view similar to that of FIG. 11A illustratinganother step in the method in which the ablated tissue volume is shown.

FIG. 12 is a sectional view of an alternate working end similar to thatof FIG. 3 in a method of use, the dielectric structure having a centralsupport member functioning as (i) an electrode and as (ii) a gas flowdirecting means.

FIG. 13 is a block diagram of one method corresponding to the invention.

FIG. 14 is a block diagram of another method corresponding to theinvention.

FIG. 15 is a block diagram of another method corresponding to theinvention.

FIG. 16 is a block diagram of another method corresponding to theinvention.

FIG. 17 is a block diagram of another method corresponding to theinvention.

FIG. 18A is a sectional view of a working end of an ablation probesimilar to that of FIG. 12 with an expandable thin-wall dielectricstructure in a non-extended condition.

FIG. 18B is a sectional view of the working end of FIG. 18A with theexpandable thin-wall dielectric structure in an extended condition insoft tissue, the structure configure for expansion by gas inflationpressure.

FIG. 18C is another sectional view as in FIG. 18B showing the capacitivecoupling of energy to the tissue from a contained plasma in theexpandable dielectric structure.

FIG. 18D is another sectional view as in FIG. 18B showing the region ofablated tissue after energy delivery.

FIG. 19 is another cross-sectional view of the expandable dielectricstructure in a non-extended condition folded within a translatablesheath.

FIG. 20 is a cut-away schematic view of a heart and a working end ofanother ablation probe similar to that of FIG. 18A with an expandablethin-wall dielectric structure configured for ablating about a pulmonaryvein to treat atrial fibrillation, with the structure configure forexpansion by gas inflation pressure.

FIG. 21 is an enlarged sectional schematic view of the working end ofFIG. 20 ablating a pulmonary vein.

FIG. 22 is a cut-away schematic view of a heart and deflectable workingend of another ablation probe configured for ablating a linear lesion totreat atrial fibrillation.

FIG. 23 is a schematic perspective view of the deflectable working endof FIG. 22 illustrating an elongate dielectric structure.

FIG. 24 is a cross-sectional view of the deflectable working end anddielectric structure of FIG. 23 illustrating an interior electrode.

FIG. 25 is a perspective view of another deflectable working end similarto that of FIGS. 23-24 for creating a circumferential lesion to treatatrial fibrillation.

FIG. 26 is a cut-away schematic view of a esophagus and working end ofanother ablation probe similar to that of FIG. 20 with an expandablethin-wall dielectric structure configured for expansion by an interiorskeletal framework.

FIG. 27 is a cut-away view of the expandable thin-wall dielectricstructure of FIG. 26 showing the interior skeletal support frame thatoptionally functions as an electrode.

FIG. 28 is a cut-away view of another expandable dielectric structuresimilar to FIG. 27 showing an alternative interior skeletal supportframe.

FIG. 29 is a sectional schematic view of a working end of anotherablation probe comprising first and second opposing jaws engaging tissuewith each jaw engagement surface including a thin-wall dielectricstructure, the jaws configured for sealing or coagulating tissue clampedtherebetween.

FIG. 30 is a schematic view of the working end of another embodimentwith an expandable thin dielectric walled structure with a plurality ofplasma-carrying chambers for performing another form of bi-polarablation.

FIG. 31 is a transverse sectional schematic view of the working end ofFIG. 30 taken along line 31-31 of FIG. 36 rotated 90° showing thecurrent flow in tissue.

FIG. 32 is a cut-away view of another type of working end with compliantenergy-delivery surface carrying and integrated stretchable knitelectrode structure.

FIGS. 33A-33B are schematic views of a method of making the working endof FIG. 32; wherein FIG. 33A depicts a conductive knit structuredisposed over a core pin; and wherein FIG. 33B depicts the core pin andconductive knit structure in an injection mold with an elastomerinjected into the mold.

FIG. 34 includes an enlarged schematic views of the complaint surface ofthe working end of FIG. 32 and FIGS. 33A-33B illustrating exposedportions of the conductive knit structure that function as RFelectrodes.

FIG. 35 illustrates an alternative form of a conductive yarn that can beused in the knit structure of FIG. 34.

FIG. 36 is a plan view of an alternative working end similar to that ofFIG. 32; the working end configured for performing an endometrialablation.

FIG. 37 is a schematic view of another compliant energy-delivery surfaceillustrating that the technical knit can provide varied exposedelectrode portions following injection molding.

FIG. 38 is a view of an alternative working end configured forperforming an endometrial ablation with regions of the working endconfigured for providing different depths of ablation.

DETAILED DESCRIPTION OF THE INVENTION

Several embodiments of ablation systems useful for practicing ablationmethods corresponding to the present invention are shown in thedrawings. In general, each of these embodiments utilizes a neutral gascontained within a chamber that is at least partly enclosed by thin-walldielectric enclosure, wherein the dielectric wall provides forcapacitive coupling of RF current from the gas to through the dielectricto contacted tissue. A second electrode is in contact the tissue at anexterior of the dielectric enclosure. The system embodiments typicallyinclude an instrument with a working end including the thin-walldielectric enclosure for containing an ionizable gas. Current flow tothe tissue initiates when sufficient voltage is applied to ionize thecontained gas into a plasma and the contemporaneous capacitive couplingthrough the surrounding dielectric structure occurs. The invention thusprovides a voltage-based electrosurgical effect that is capable ofablating tissue to a controlled depth of 1 mm to 5 mm or more veryrapidly, wherein the depth of ablation is very uniform about the entiresurface of the dielectric enclosure. The instrument working end anddielectric enclosure can take a variety of forms, including but notlimited to an elongated shaft portion of a needle ablation device, adielectric expandable structure, an articulating member, a deflectablemember, or at least one engagement surface of an electrosurgical jawstructure. The system embodiments and methods can be used forinterstitial tissue ablation, intraluminal tissue ablation or topicaltissue ablation.

The system embodiments described herein utilize a thin-wall dielectricstructure or wall at an instrument working end that contains anelectrically non-conductive gas as a dielectric. The thin-walldielectric structure can be a polymer, ceramic or glass with a surfaceconfigured for contacting tissue. In one embodiment, an interior chamberwithin the interior of the thin-wall dielectric structure carries acirculating neutral gas or static neutral gas such as argon. An RF powersource provides current that is coupled to the neutral gas flow orstatic gas volume by an electrode disposed within the interior of theworking end. The gas flow or static gas contained within the dielectricenclosure is of the type that is non-conductive until it has beentransformed to a conductive plasma by voltage breakdown. The thresholdvoltage for breakdown of the gas will vary with variations in severalparameters, including the gas pressure, the gas flow rate, the type ofgas, and the distance from the interior electrode across the interiorchamber to the dielectric structure. As will be seen in some of theembodiments, the voltage and other operational parameters can bemodulated during operation by feedback mechanisms.

The gas, which is ionized by contact with a conductive electrode in theinstrument working end, functions as a switching mechanism that onlypermits current flow into targeted tissue when the voltage across thecombination of the gas, the dielectric structure and the contactedtissue reaches a predetermined threshold potential that causescapacitive coupling across the dielectric structure. By this means ofpermitting current flow only at a high threshold voltage thatcapacitively couples current to the tissue, the invention allows asubstantially uniform tissue effect within all tissue in contact withthe dielectric structure. Further, the invention allows the ionized gasto be created contemporaneously with energy application to tissue by theconversion of a non-conductive gas to a plasma.

In one embodiment of the apparatus, the ionized gas functions as anelectrode and comprises a gas flow that can conduct current across aninternal contained volume of the gas within a dielectric structure,typically from an electrode at an interior of a working end in contactwith the gas flow. The gas flow is configured for the purpose ofcoupling energy to the dielectric structure uniformly across the surfaceof the dielectric structure, but that will only conduct such energy whenthe non-conductive gas media has been transformed to a conductive plasmaby having been raised to a threshold voltage.

DEFINITIONS

Plasma. In general, this disclosure may use the terms “plasma” and“ionized gas” interchangeably. A plasma consists of a state of matter inwhich electrons in a neutral gas are stripped or “ionized” from theirmolecules or atoms. Such plasmas can be formed by application of anelectric field or by high temperatures. In a neutral gas, electricalconductivity is non-existent or very low. Neutral gases act as adielectric or insulator until the electric field reaches a breakdownvalue, freeing the electrons from the atoms in an avalanche process thusforming a plasma. Such a plasma provides mobile electrons and positiveions, an acts as a conductor which supports electric currents and canform spark or arc. Due to their lower mass, the electrons in aplasmaaccelerate more quickly in response to an electric field than theheavier positive ions, and hence carry the bulk of the current. Avariety of terms are known in the literature to describe a transientplasma discharge across a gas such as plasma filament, plasma streamer,plasma microstreamer, plasma wire or plasma hair. In this disclosure,the terms plasma filament and plasma streamer are used interchangeablyherein to describe visible plasma discharges within and across a gasvolume. A plasma filament may also be called a dielectric barrierdischarge herein when describing a plasma filament generated adjacentto, and as a function of, high voltage current coupling through adielectric wall.

Dielectric and dielectric loss. The term dielectric is used in itsordinary sense meaning a material that resists the flow of electriccurrent, that is, a non-conducting substance. An important property of adielectric is its ability to support an electrostatic field whiledissipating minimal energy in the form of heat. The lower the dielectricloss (the proportion of energy lost as heat), the more effective is adielectric material.

Dielectric constant or relative permittivity. The dielectric constant(k) or relative static permittivity of a material under given conditionsis a measure of the extent to which it concentrates electrostatic linesof flux, or stated alternatively is a number relating the ability of thematerial to carry alternating current to the ability of vacuum to carryalternating current. The capacitance created by the presence of amaterial is directly related to its dielectric constant. In general, amaterial or media having a high dielectric constant breaks down moreeasily when subjected to an intense electric field than do materialswith low dielectric constants. For example, air or another neutral gascan have a low dielectric constant and when it undergoes dielectricbreakdown, a condition in which the dielectric begins to conductcurrent, the breakdown is not permanent. When the excessive electricfield is removed, the gas returns to its normal dielectric state.

Dielectric breakdown. The phenomenon called dielectric breakdown occurswhen an electrostatic field applied to a material reaches a criticalthreshold and is sufficiently intense so that the material will suddenlyconduct current. In a gas or liquid dielectric medium, this conditionreverses itself if the voltage decreases below the critical point. Insolid dielectrics, such a dielectric breakdown also can occur and coupleenergy through the material. As used herein, the term dielectricbreakdown media refers to both solid and gas dielectrics that allowcurrent flow across the media at a critical voltage.

Degree of ionization. Degree of ionization describes a plasma'sproportion of atoms which have lost (or gained) electrons, and iscontrolled mostly by temperature. For example, it is possible for anelectrical current to create a degree of ionization ranging from lessthan 0.001% to more than 50.0%. Even a partially ionized gas in which aslittle as 0.1% or 1.0% of the particles are ionized can have thecharacteristics of a plasma, that is, it can strongly respond tomagnetic fields and can be highly electrically conductive. For thepurposes of this disclosure, a gas may begin to behave like conductiveplasma when the degree of ionization reaches approximately 0.1%, 0.5% or1.0%. The temperature of a plasma volume also relates to the degree ofionization. In particular, plasma ionization can be determined by theelectron temperature relative to the ionization energy. A plasma issometimes referred to as being “hot” if it is nearly fully ionized, or“cold” or a “technological plasma” if only a small fraction (forexample, less than 5% or less than 1%) of the gas molecules are ionized.Even in such a cold plasma, the electron temperature can still beseveral thousand degrees Celsius. In the systems according to thepresent invention, the plasmas are cold in this sense because thepercentage of ionized molecules is very low. Another phrase used hereinto describe a “cold” plasma is “average mass temperature” of the plasmawhich relates to the degree of ionization versus non-ionized gas andwhich averages the temperatures of the two gas volume components. Forexample, if 1% of a gas volume is ionized with an electron temperatureof 10,000° C., and the remaining 99% has a temperature of 150° C., thenthe mass average temperature will be 149.5° C. It has been found thatmeasuring the plasma temperature can be used to determine an approximatedegree of ionization which can be used for feedback control of appliedpower, and as a safety mechanism for preventing unwanted hightemperatures within a thin-wall dielectric structure.

Referring to FIG. 1, a first embodiment of a tissue ablation system 100utilizing principles of the present invention is shown. The system 100includes a probe 110 having a proximal handle 112 and an elongated shaftor extension member 114 that extends along axis 115. The handle 110 isfabricated of an electrically insulative material such as a plastic,ceramic, glass or combination thereof. The extension member 114 has aproximal end 116 coupled to handle 112. The extension member 114 extendsto a distal working end 120 that includes a dielectric member orstructure 122 that is configured for contacting tissue that is targetedfor ablation.

In the embodiment of FIG. 1, the working end 120 and dielectricstructure 122 is elongated and cylindrical with a cross-section rangingfrom about 0.5 mm to 5 mm or more with a length ranging from about 1 mmto 50 mm. The cross-section of the working end 120 can be round, oval,polygonal, rectangular or any other cross-section. As can be seen inFIGS. 2A-2B, in one embodiment, the working end 120 has a sharp tip 124for penetrating tissue to perform an ablation procedure, such asablating a tumor indicated at 125 in a tissue volume 130. In otherembodiment, the distal tip of a working end 120 can be blunt. In yetother embodiment, the entire working end can have a guide channeltherein for advancing the working end over a guide wire.

Now turning to FIG. 3, an enlarged view of the working end 120 of FIGS.1, 2A and 2B is shown. It can be seen that the dielectric structure 122has a thin wall 132 that provides an enclosure about an interior chamber135 that contains a gas media indicated at 140 in FIG. 3. In oneembodiment, the dielectric structure 122 can comprise a ceramic (e.g.,alumina) that has a dielectric constant ranging from about 3 to 4. Thethickness of wall 132 can range from 0.002″ to 0.10″ depending on thediameter, or more typically 0.005″ to 0.050″ in a diameter ranging from1 to 4 mm. In other embodiment shown in FIG. 4A, the dielectricstructure 122 can comprise a ceramic, glass or polymer in a molded formwith strengthening support portions 142 or ribs that end axially,radially, helically or a combination thereof. The support portions 142alternatively can comprise members that are independent of a thin-wall132 of a dielectric material. In such an embodiment (FIG. 4A) as will bedescribed below, the thin wall portions 144 of the dielectric structure122 permit capacitive coupling of current to tissue while the supportportions 142 provide structural strength for the thin-wall portions 144.In another embodiment, a portion of which is shown in FIG. 4B, thedielectric structure 122 has support portions 142 in a waffle-likeconfiguration wherein thin-wall portions 144 are supported by thickerwall support portions 142. The waffle-like structure can besubstantially planar, cylindrical or have any other suitableconfiguration for containing a gas dielectric in a chamber indicated at135 on one side of the dielectric structure 122. In another embodimentof FIGS. 5A and 5B, the dielectric structure 122 can have supportportions 142 comprising posts that support the thin-wall portions 144over another supporting member 145. The planar dielectric structure 122can be used, for example, in planar jaw members for applying RF energyto seal tissue. In another example, FIG. 5B shows a blunt-tipped,cylindrical thinwall 132 of a dielectric structure 122 supported by acore supporting member 145. In the embodiment of FIG. 5B, the interiorchamber 135 which can contain a plasma comprises a space between thethin wall portions 144 and the core support member 145.

Referring again to FIG. 3, the extension member 114 is fabricated of anelectrically non-conductive material such as polymer, ceramic, glass ora metal with an insulative coating. The dielectric structure 122 can bebonded to extension member 114 by glues, adhesives or the like toprovide a sealed, fluid-tight interior chamber 135. In one embodiment, agas source 150 can comprise one or more compressed gas cartridges (FIGS.1 and 6). As will be described below (FIG. 6), the gas source is coupledto a microcontroller 155 that includes a gas circulation subcontroller155A which controls a pressure regulator 158 and also controls anoptional negative pressure source 160 adapted for assisting incirculation of the gas. The RF and controller box 162 in FIG. 1 caninclude a display 164 and input controls 165 for setting and controllingoperational parameters such as treatment time intervals, gas flows,power levels etc. Suitable gases for use in the system include argon,other noble gases and mixtures thereof.

Referring to FIG. 3, the gas source 150 provides a flow of gas media 140though a flexible conduit 166 to a first flow channel 170 in extensionmember 114 that communicates with at least one inflow port 172interfacing with interior chamber 135. The interior chamber 135 alsointerfaces with an outflow port 174 and second flow channel 180 inextension member 114 to thereby allow a circulating flow of gas media140 within the interior of dielectric structure 122.

Still referring to FIG. 3, a first polarity electrode 185 is disposedabout flow channel 170 proximate to the inflow port 172 thus being incontact with a flow of gas media 140. It should be appreciated thatelectrode 185 can be positioned in any more proximal location in channel170 in contact with the gas flow, or the electrode 185 can be withininterior chamber 135 of dielectric structure 122. The electrode 185 iselectrically coupled to a conductor or lead 187 that extends through theextension member and handle 112 and is coupled to a first pole of a highfrequency RF generator 200 which is controlled by controller 155 and RFsubcontroller 155B. An opposing polarity electrode 205 is disposed onthe exterior surface of extension member 114 and is electrically coupledby lead 207 to a second pole of RF generator 200.

The box diagrams of FIGS. 6 and 7 schematically depict the system,subsystems and components of one embodiment that is configured fordelivering ablative electrosurgical energy to tissue. In the box diagramof FIG. 6, it can be seen that an RF power source 200 and circuit iscontrolled by RF subcontroller 155B. Feedback control subsystems(described below) based on systems and probe pressure feedback, probetemperature feedback, and/or gas flow rate feedback are also operativelycoupled to controller 155. The system can be actuated by footswitch 208or another suitable switch. FIG. 7 shows a schematic of the flow controlcomponents relating to the flow of gas media through the system andprobe 110. It can be seen that a pressurized gas source 150 in linked toa downstream pressure regulator 158, an inflow proportional valve 210,flow meter 212 and normally closed solenoid valve 220. The valve 220 isactuated by the system operator which then allows a flow of gas media140 to circulate through flexible conduit 166 and probe 110. The gasoutflow side of the system includes a normally open solenoid valve 225,outflow proportional valve 226 and flowmeter 228 that communicate withnegative pressure source 160. The exhaust of the gas can be into theenvironment or into a containment system. A temperature sensor 230(e.g., thermocouple) is shown in FIG. 7 for monitoring the temperatureof outflow gases.

FIGS. 8 and 9A-9D schematically illustrate a method of the inventionwherein (i) the dielectric structure 122 and (ii) the contained neutralgas volume 140 function contemporaneously to provide first and seconddielectric media that cooperatively function as independent mechanismsto couple high voltage current to tissue in contact with the thin-walldielectric 132. The two dielectric components can be characterized ashaving complementary voltage thresholds levels at which only highvoltage current can couple through a plasma filament or streamer 235 inplasma 240 within chamber 135 and capacitively couple through thethin-wall dielectric 132 to allow a current to further pass through aleast resistive path 245 in the engaged tissue. In FIG. 8, the engagedtissue is assumed to be surrounding the dielectric structure 122 and istransparent. In the embodiment of FIG. 8, the electrode 185 is tubularand functions and a gas delivery sleeve wherein a neutral gas 140 canexit ports 250 in chamber 135. The high voltage current paths 245 inplasma filaments scan or move across and about the inner surface 248 ofthe dielectric structure 122 and within paths in the contacted tissuewhich can deliver a voltage-maximized current causing Joule heating inthe tissue. FIG. 8 provides a schematic view of what is meant by theterminology or plasma filament “scanning” the interior surface of thedielectric 132 wherein high intensity electrical fields are produced ininterior chamber 135 of dielectric structure 122 by capacitive couplingthrough the dielectric wall 132 until a voltage threshold is reached inthe neutral gas media 140 to convert the gas into a plasma 240 (see FIG.8) which in turn allows plasma filaments 235 to form within the chamber135 which randomly move or scan about the interior surface 248 of thedielectric wall. In one embodiment, movement or scanning of such plasmafilaments 235 within the chamber 135 (from electrode 185 to innersurface 248 of dielectric wall 132) is spatiotemporally chaotic and thedischarge occurs where there is a transient, reversible voltagebreakdown in a localized portion 252 of the dielectric wall 132, whichis determined by a transient highest conduction path 240 in engagedtissue to the second polarity electrode 205 (FIG. 3). An instant afterthe flow of current through the plasma 240 and path 245 in tissue, thelocalized portion 252 dissipates the electrical field and anothercapacitive coupling occurs through another plasma filament 235′ andcurrent path 245′ in tissue to cause electrosurgical ablation in anotherrandom, discrete location. In another embodiment, the plasma filamentscan be very fine resulting in the appearance of a glow discharge withinchamber 135 instead of spaces apart discrete plasma filaments.

FIGS. 9A-9D are enlarged schematic illustrations of the electrosurgicalablation method of FIG. 8 that depict other aspects of the ablationmethod. In FIG. 9A, it can be seen that the system and method isgeneralized to show clearly the first and second dielectric currenttransmission mechanisms characterized by selected voltage parameters tocause an electron avalanche in the gas and capacitive coupling in thethin-wall enclosure to optimize and maximize a form of high voltagecurrent delivery to an exemplary tissue 260. As described previously,the voltage threshold or dielectric breakdown mechanisms occur within(i) the gas dielectric or neutral gas volume 140 that is containedwithin an interior chamber 135 of dielectric structure 122 and (ii) thenon-gas dielectric or structure 122 shown as a plane in FIGS. 9A-9D.

FIG. 9A illustrates the working end components and tissue 260 prior tothe actuation and delivery of energy to the tissue. It can be seen thatthe gas media 140 is neutral and not yet ionized. The first polarityelectrode 185 positioned in the interior chamber 135 in contact withneutral gas 140 is shown schematically. The second polarity electrode205 in contact with tissue is also shown schematically, but theillustration represents another aspect of the invention in that thesecond electrode 205 can have a small surface area compared to thesurface areas of return electrodes/ground pads as in conventionalelectrosurgical systems. It has been found that the capacitively coupledenergy delivery mechanism of the invention does not cause tissue heatingat or about the surface of the second polarity electrode 205 as would beexpected in a conventional electrosurgical device. As will be describedbelow, it is believed that the constant flux in voltagebreakdown-initiated and capacitive coupling-initiated current paths inthe tissue 260 greatly reduces heat built up at or about the returnelectrode 205.

FIG. 9B illustrates the working end components and tissue 260 at aninstant in time immediately after the operator actuates the system anddelivers power to the probe working end. Several aspects of thevoltage-initiated breakdown ablation method are represented in FIG. 9B,including (i) in one aspect of the instant in time, the neutral gas 140is converted to a plasma 240 by potential between the first and secondpolarity electrodes 185 and 205; and contemporaneously (ii) current flowdefines a least resistive path 245 in the tissue 260; (iii) a portion252 of dielectric structure 122 adjacent current path 245 allowscapacitive coupling to the tissue; (iv) the plasma filament 235 arcsacross a high intensity plasma stream 262 between electrode 185 and theportion 252 of the dielectric structure. In other words, when the aselected voltage potential is reached, the voltage breakdown of the gas140 and capacitively coupling through the dielectric 122 causes a highvoltage current to course through path 245 in the tissue 260. An instantlater, thermal diffusion indicated by arrows 265 causes thermal effectsin a tissue volume 270 a outward from the transient current path 245.The thermal effects in and about path 245 elevates tissue impedance,which thus causes the system to push a conductive path to another randomlocation.

FIG. 9C illustrates the working end components and tissue 260 an instantafter that of FIG. 9B when continued voltage potential causes voltagebreakdown in plasma filament 235′ together with capacitively couplingthrough dielectric 122 to provide another high voltage current to coursethrough path 245′ after which heat diffusion 265′ causes thermal effectsindicated at 270 b. The “scanning” aspect of the ablation method can beunderstood from FIGS. 9A-9B wherein the plasma filaments 235, 235′ andcurrent paths very rapidly jump or scan about the interior chamber 135to thereby deliver current in a path of least resistance 245, 245′ inthe tissue 260.

Now turning to FIG. 9D, another schematic is shown following an intervalof energy delivery in which a multiplicity of current paths through thepre-existing plasma and dielectric 122 have provided thermal effectsdiffused throughout a multiplicity of regions indicated at 270 a-270 f.By this method, it has been found that ablation depths of 3 mm to 6 mmcan be accomplished very rapidly, in for example 30 seconds to 90seconds dependent upon the selected voltage.

In one aspect of the invention, FIG. 10 is a circuit diagramrepresenting the steps of the method of FIGS. 9A-9D which explains thediscovery that return electrode 205 can have a small surface area andnot be subject to significant heating. In FIG. 10, it can be seen thatvoltage potential can increase until a dielectric breakdown occurs inboth the neutral gas 140 and the dielectric structure 122 which cause ahigh voltage current through path P1 to electrode 205, followed by thatpath impeding out, thus causing the current to shift to current path P2,then current path P3 ad infinitum to current path indicated at Pn. Thetissue 260 in FIG. 10 thus is shown as variable resistor in each currentpath as the current path is in continual flux based on the pathincreasing in resistance.

FIGS. 11A and 11B are enlarged schematic illustrations of the method ofusing the embodiment of FIG. 3 to capacitively couple current to tissuewith a gas dielectric 140 in interior chamber 135 (i.e., plasmaindicated at 240). Referring to FIG. 11A, the system is actuated, forexample by a footswitch 208 (FIG. 1) coupled to RF power source 200 andcontrollers 155A and 155B which initiates a gas flow from source 150 toprovide circulating flow through the first (inflow) channel 170,interior chamber 135 and the second (outflow) channel 180. Forconvenience, the embodiments utilizing such a circulating gas flow willbe described herein as using one preferred gas, which is argon. In oneembodiment, the gas flow rate can be in the range of 1 ml/sec to 50ml/sec, more typically from 5 ml/sec to 30 ml/sec. In FIG. 11A, theworking end 120 of the probe is introduced into tissue 260, for exampleto ablate a tumor as in FIGS. 2A-2B. The dielectric structure 122 ispositioned in a desired location to ablate tissue adjacent thereto. Theactuation of the system contemporaneously applies RF energy to electrode185 and the gas flow which instantly converts the non-conductive argon140 to a plasma indicated at 240 in FIG. 11A. The threshold voltage atwhich the argon becomes conductive (i.e., converted in part into aplasma) is dependent upon a number of factors controlled by thecontroller, including the pressure of the argon gas, the volume ofinterior chamber 135, the flow rate of the gas 140, the distance betweenelectrode 185 and interior surfaces of the dielectric surface 122, thedielectric constant of the dielectric structure 122 and the selectedvoltage applied by the RF power source 200. It should be appreciatedthat the actuation of the system can cause gas flows for an interval of0.1 to 5 seconds before the RF generator powers on to insure circulatorygas flows.

FIG. 11A schematically depicts current indicated at 280 beingcapacitively coupled through the wall 132 of the dielectric structure122 to tissue 260, with the electric field lines indicating that highenergy densities do not occur about electrode 205. Rather, as describedabove, the high resistance developed in tissue about the current pathdielectric structure 122 causes rapidly changing current paths and ohmicheating. In one aspect of the invention, the capacitive coupling allowsfor rapid, uniform ablation of tissue adjacent the dielectric structure.FIG. 11B schematically depicts the tissue after the RF energy deliveryis terminated resulting in the ablated tissue indicated at 285.

Now turning to FIG. 12, an alternate working end 120′ is shown in amethod of use. In this embodiment, the dielectric structure 122 issimilar to that of FIG. 3 except the working end 120′ includes a centralsupport member 290 that extends from extension member 214 to a distaltip portion 292. In this embodiment, the central support member 290 cancomprise, or carry, a conductive electrode surface indicated at 295 todelivery energy to the gas 140 in interior chamber 135 for creating theplasma. The embodiment of FIG. 12 also includes concentric gas inflowand outflow channels, 170 and 180, wherein the first (inflow) channel170 comprises a lumen in support member 290 that communicates with aplurality of flow outlets 250 in a distal portion of interior chamber135. The gas outflow port 174 is again disposed in a proximal portion ofinterior chamber 135. The placement of gas inflow and outflow ports inopposing ends of interior chamber allows for effective gas circulationwhich assists in maintaining a predetermined plasma quality. In FIG. 12,the ablative currents and ohmic heating in tissue are indicated at 200.

In another aspect of the invention, FIG. 12 illustrates that at leastone temperature sensor, for example thermocouples 300A and 300B, areprovided within or adjacent to interior chamber 135 to monitor thetemperature of the plasma. The temperature sensors are coupled tocontrollers 155A and 155B to thus allow feedback control of operatingparameters, such a RF power delivered, neutral gas inflow rate, andnegative pressure that assists outflow. By measuring the mass averagetemperature of the media in chamber 135, the degree of ionization of theionized gas 240 can be determined. In one aspect of the invention, themeasured temperature within chamber 135 during operation can providefeedback to gas circulation controller to thereby modulate the flow ofneutral gas to maintain a degree of ionization between 0.01% and 5.0%.In another aspect of the invention, the measured temperature withinchamber 135 during operation can provide feedback to modulate flow ofneutral gas to maintain a temperature of less than 200° C., 180° C.,160° C., 140° C., 120° C., or 100° C. In several embodiments ofpolymeric dielectric structures, it is important to maintain a cold ortechnological plasma to prevent damage to the dielectric. In anotheraspect of invention, the system operating parameters can be modulated tomaintain the mass average temperature within a selected range, forexample a 5° C. range, a 10° C. range or a 20° C. range about a selectedtemperature for the duration of a tissue treatment interval. In anotheraspect of invention, the system operating parameters can be modulated tomaintain a degree of ionization with less than 5% variability, less than10% variability or less than 20% variability from a selected “degree ofionization” target value for a tissue treatment interval. While FIG. 12shows thermocouples within interior chamber 135, another embodiment canposition such temperature sensors at the exterior of the wall 132 of thedielectric structure to monitor the temperature of the wall. It alsoshould be appreciated that multiple electrodes can be provided in theinterior chamber to measure impedance of the gas media to provide anadditional from of feedback signals.

In another embodiment similar to FIG. 12, the working end or flowchannel in communication with the interior chamber 135 can carry atleast one pressure sensor (not shown) and pressure measurement canprovide feedback signals for modulating at least one operationalparameter such as RF power delivered, neutral gas inflow rate, negativepressure that assists outflow, degree of ionization of the plasma, ortemperature of the plasma. In another aspect of invention, the systemoperating parameters can be modulated to maintain a pressure withinchamber 135 less than 5% variability, less than 10% variability or lessthan 20% variability from a selected target pressure over a tissuetreatment interval.

In general, FIG. 13 represents the steps of a method corresponding toone aspect of the invention which comprises containing a non-conductivegas in an interior of an enclosure having a thin dielectric wall,engaging and external surface of the dielectric wall in contact with atarget region of tissue, and applying a radiofrequency voltage acrossthe gas and the dielectric wall wherein the voltage is sufficient toinitiate a plasma in the gas and capacitively couple current in the gasplasma across the dielectric wall and into the engaged tissue. Thismethod includes the use of a first polarity electrode in contact withthe gas in the interior of the thin dielectric wall and a secondpolarity electrode in contact with the patient's tissue.

FIG. 14 represents aspects of a related method corresponding to theinvention which comprises positioning a dielectric structure on a tissuesurface, containing a non-conductive, ionizable gas within thedielectric structure, and applying RF voltage across the gas and tissueto ionize the gas and deliver current through the dielectric structureto the tissue to ohmically heat the tissue.

In general, FIG. 15 represents the steps of a method corresponding toanother aspect of the invention which comprises providing anelectrosurgical working end or applicator with a first gas dielectricand a second non-gas dielectric in a series circuit, engaging thenon-gas dielectric with tissue, and applying sufficient RF voltageacross the circuit to cause dielectric breakdown in the gas dielectricto thereby apply ablative energy to the tissue. The step of applyingablative energy includes capacitively coupling RF current to the tissuethrough the second non-gas dielectric media.

FIG. 16 represents steps of another aspect of the invention whichcomprises positioning a dielectric structure enclosing an interiorchamber in contact with targeted tissue, providing a gas media in theinterior chamber having a degree of ionization of at least 0.01%, andapplying RF current through the gas media to cause capacitive couplingof energy through the dielectric structure to modify the tissue. In thisaspect of the invention, it should be appreciated that an ionized gascan be provided for inflow into chamber 135, for example with a neutralgas converted to the ionized gas media prior to its flow into chamber135. The gas can be ionized in any portion of a gas inflow channelintermediate the gas source 150 and the interior chamber 135 by an RFpower source, a photonic energy source or any other suitableelectromagnetic energy source.

FIG. 17 represents the steps of another method of the invention whichcomprises positioning a dielectric structure enclosing a gas media incontact with targeted tissue, and applying RF current through the gasmedia and dielectric structure to apply energy to tissue, and sensingtemperature and/or impedance of the ionized gas media to providefeedback signals to thereby modulate a system operational parameter,such as RF power delivered, neutral gas inflow rate, and/or negativepressure that assists gas outflows.

FIGS. 18A-18D illustrate another embodiment of electrosurgical system500 and working end 520 and method of use that is similar to the deviceof FIG. 12 except that the dielectric structure 522 of FIGS. 18A-18D isfabricated of a thin-wall dielectric that can be moved from a firstnon-expanded condition to an expanded condition. In FIG. 18A, theworking end is shown with a distally-extended sheath 524 that can be ofplastic or metal. A first step of a method thus comprises introducingthe working end into tissue interstitially or into a body lumen with thesheath protecting the dielectric structure 522. The dielectric structure522 is then expanded by gas inflows which causes compression ofsurrounding tissue and increases the surface area of the thin dielectricwall in contact with tissue. As can be seen in FIG. 18A, the expandabledielectric 522 can be fabricated of a distensible or non-distensiblematerial, such as a stretchable silicone or a braided, reinforcednon-stretch silicone. The wall thickness of a silicone structure canrange from 0.004″ to 0.030″, and more typically from 0.008″ to 0.015″with an interior volume ranging from less that 5 ml to more than 100 ml.The dielectric structure can have any suitable shape such ascylindrical, axially tapered, or flattened with interior baffles orconstraints. FIG. 19 depicts a cross-section of the sheath 524 and anon-distensible expandable dielectric 522 with a method of folding thethin dielectric wall.

FIG. 18B illustrates multiple subsequent steps of the method whereinsheath 524 is retracted and the physician actuates the gas source 150and controller to expand the expandable dielectric structure 522. Thestructure 522 or balloon can be expanded to any predetermined dimensionor pressure in soft tissue or in any body lumen, cavity, space orpassageway. Radiopaque marks on the dielectric structure (not shown) canbe viewed fluoroscopically to determine its expanded dimension andlocation. The gas circulation controller 155A can circulate gas flowafter a predetermined pressure is achieved and maintained.

FIG. 18C depicts a subsequent step of the method in which the physicianactuates the RF power source 200 and controller 155B to develop highvoltage potential between central support electrode 295 and returnelectrode 205 which, as described previously, can cause a voltagebreakdown in the gas dielectric 140 (FIG. 18B) to create plasma 240 andcontemporaneously capacitively couple current to tissue 260 as indicatedby current flows 530. FIG. 18D depicts the termination of RF energydelivery so that the voltage breakdown and resulting plasma isextinguished—leaving uniform ablated tissue 540 similar to that shown inFIG. 11B.

In one embodiment, the dielectric structure 522 was made from NuSilMED-6640 silicone material commercially available from NuSil TechnologyLLC, 1050 Cindy Lane, Carpinteria, Calif. 93013. The dielectricstructure 522 was fabricated by dipping to provide a length of 6 cm anda uniform wall thickness of 0.008″ thereby providing a relativepermittivity in the range of 3 to 4. The structure ends were bonded to ashaft having a diameter of approximately 4 mm with the expandedstructure having an internal volume of 4.0 cc's. The gas used was argon,supplied in a pressurized cartridge available from Leland Limited, Inc.,Post Office Box 466, South Plainfield, N.J. 07080. The argon wascirculated at a flow rate ranging between 10 ml/sec and 30 ml/sec.Pressure in the dielectric structure was maintained between 14 psia and15 psia with zero or negative differential pressure between gas inflowsource 150 and negative pressure (outflow) source 160. The RF powersource 200 had a frequency of 480 KHz, and electrical power was providedwithin the range of 600 Vrms to about 1200 Vrms and about 0.2 Amps to0.4 Amps and an effective power of 40 W to 80 W.

FIGS. 20 and 21 illustrate another embodiment of electrosurgical system600 that comprises a catheter having working end 610 for treating atrialfibrillation by means of ablation about pulmonary veins PV. Variousmethods of using conventional RF catheters for such treatments areknown. Catheter 610 is configured with a guidewire channel 612 and canbe navigated to a site shown in FIGS. 20-21. The catheter working end620 included an expandable dielectric structure 622 similar to that ofFIGS. 18A-18D that can be expanded to apply pressure between the balloonwall and the tissue to thereafter create a circumferential lesion in apulmonary vein PV. FIG. 21 is a schematic illustration that again showsgas source 150 and gas circulation controller 155A that can expandchamber 635 in the thin-wall dielectric structure 622 to engage the wallof the pulmonary vein PV. In the embodiment of FIG. 21, it can be seenthat the wall of dielectric 622 includes a first (lesser)energy-transmissible region 636 and a second (greater)energy-transmissible region 638 thus allowing a focused circumferentialablation wherein the dielectric has a lesser cross-section as disclosedin co-pending U.S. patent application Ser. No. 12/541,043 (AttorneyDocket No. 027980-000110US) filed on Aug. 13, 2009. Thereafter, the RFpower source 200 and controller 155B can be actuated to convert theneutral gas flow to plasma 240 and contemporaneously ablate tissueindicated at 640. In this embodiment, a first polarity electrode 645 isprovided on the catheter shaft in chamber 635 that can cooperate with asecond polarity electrode on the catheter shaft remote from balloon 622or any other type of ground pad may be used (not shown). In all otherrespects, the method of the invention for ablation of cardiac tissuefollows the steps described above. The balloon can have radiopaquemarkings, and the system can be operated by an algorithm to expand thedielectric structure 622 or balloon to a pre-determined pressure, thendelivery RF energy and terminate delivery automatically. It should beappreciated that additional electrodes can be provided in the balloonsurface (not shown) for mapping conduction in the cardiac tissue.

While FIG. 20-21 illustrate an expandable dielectric 622 for treatingcardiac tissue, it should be appreciate that the scope of the inventionincludes using a similar apparatus and method to controllably applyablative RF energy to any body lumen, vessel, body cavity or space suchas in a stomach, gall bladder, esophagus, intestine, joint capsule,airway, sinus, a blood vessel, an arteriovascular malformation, heart,lung, uterus, vaginal canal, bladder or urethra.

FIGS. 22-24 schematically illustrate another embodiment ofelectrosurgical system 700 and catheter having working end 710 fortreating atrial fibrillation with linear lesions within a heart chamberto block aberrant conduction pathways. Catheter 710 can have a guidewirechannel (not shown) and can be navigated to perform an elongatedablation in a heart chamber as in FIG. 22. In this embodiment, thecatheter working end 720 has a flexible shaft portion 721 that includedan axially-extending thin-wall dielectric 722 in one surface forengaging tissue to provide a linear lesion as depicted in FIG. 24. Thecatheter shaft 721 is deflectable by means of a pull-wire 728 that canbe actuated from a catheter handle. FIG. 23 is another schematicillustration that shows the gas source 150 and gas circulationcontroller 155A that can provide gas circulation within interior chamber735 interior of the thin-wall dielectric 722. The RF power source 200 iscoupled to a lead 738 and elongated first polarity electrode 740 in theinterior chamber 735. The RF power source 200 and controller 155B can beactuated to convert the neutral gas flow to a plasma andcontemporaneously ablate tissue engaged by dielectric 722 as describedabove. The second polarity electrode can be provided on the cathetershaft remote from dielectric 722 or any type of ground pad may be used(not shown). In all other respects, the method of the invention forablation of cardiac tissue follows the steps described above. Theworking end can have radiopaque markings, and the system can be operatedin accordance with algorithms. It should be appreciated that additionalelectrodes can be provided in the catheter working end (not shown) formapping conduction in the heart pre- and post ablation.

FIG. 25 illustrates another catheter working end 720′ that is similar tothat of FIGS. 22-24 that is deflectable by a pull-wire 738 to provideall or part of circumferential lesion in a pulmonary vein (see FIGS.21-22). In this embodiment, the thin-wall dielectric 722′ extends aroundthe exterior surface of the articulated working end.

FIGS. 26 and 27 illustrate another embodiment of electrosurgical system800 that comprises a catheter having working end 810 for treating anesophagus 811, for example to ablate Barrett's esophagus, to applyenergy to lower esophageal sphincter or for other disorders. The systemoperates as previously described in FIGS. 18A-21 in embodiments thathave an expandable dielectric structure. In the dielectric structure 822of FIGS. 26-27, the expansion of the structure is provided by a skeletalsupport member such as an interior spring-like member, with an optionalpull-cable actuation mechanism. As can be seen in FIG. 27, a helicalsupport member 825 is provided that is capable of a contractedcross-section (axially-stretched) or an expanded cross-section inchamber 835 which is assisted by pulling central cable 828 in cathetershaft 830. In this embodiment, the dielectric can again comprise athin-wall silicone as described above. In this embodiment, it has beenfound that the support member 825 can be of a conductive metal andcoupled to RF power source to function as a first polarity electrode840. The second polarity electrode (not shown) can be located elsewhereon the catheter is a location in contact with tissue, or a ground padcan be used.

FIG. 28 illustrates another embodiment of electrosurgical system 800′that is similar to that of FIG. 27 with a dielectric structure 822 thatis supported in an expanded condition by a plurality of bowed-outskeletal support members 825′ that are assisted by pull-cable 828. Inthis embodiment, the portion of the pull-cable within chamber 835functions as a first polarity electrode 840′. In operation in any of theembodiments above, it has been found that the first polarity electrodecan provide sufficient voltage to create a substantially uniform plasmain an interior chamber (see FIGS. 2, 8, 11A, 21, 23, 26, 28) of anon-expandable or expandable dielectric when the surface of theelectrode is less than 15 mm, less than 10 mm or less than 5 mm from theinterior wall of the dielectric. This maximum dimension from thedielectric wall to the electrode 840′ is indicated at gap G in FIG. 28.In has also been found that, in operation, the first polarity electrodecan provide voltage to create a substantially uniform plasma in aninterior chamber of a non-expandable or expandable dielectric wall whenthe electrode contacts the surface of the dielectric 822 as in FIG. 27,but the electrode surface should engage less than about 10% of theinterior surface of the dielectric wall. If the first polarity electrodeengages greater than about 10% of the interior surface of the dielectricwall, then the “flux” of energy delivery through tissue as schematicallydepicted in FIG. 8 will be reduced, a greater capacitive coupling mayoccur about the regions of the electrode(s) in contact with the wallwhich can reduce the uniformity of tissue ablation.

FIG. 29 illustrates another embodiment of electrosurgical system 900wherein the working end 910 comprises first and second opposable jaws912A and 912B that are adapted for clamping tissue for coagulation,sealing or welding tissue 914. In one embodiment, both jaws have atissue-engaging surface that comprises a dielectric structure 922A, 922Bthat is similar in function to all other such dielectric structuresdescribed above. FIG. 29 is a schematic illustration that again showsgas source 150 and gas circulation controller 155A that can deliver gasto chambers 935A, 935B in the jaws. The RF power source 200 andcontroller 155B can be actuated to convert the neutral gas flows in thechambers 935A, 935B into plasma 240 and contemporaneously to applyenergy to engaged tissue 914. In this embodiment, the jaws carry firstand second polarity electrodes 945A and 945B, respectively, to thus makejaw function by means of a contained ionized gas and capacitivecoupling, which differs from previous embodiments. It should beappreciated that one jaw can comprise a single electrode surface, asopposed to the plasma-initiated capacitive coupling system of FIG. 29.The dielectric structures of FIG. 29 are of the type described in FIGS.4B and 5A wherein the thin-wall dielectric material is supported bysupport columns, posts, channels of the like.

FIGS. 30 and 31 illustrate another embodiment of electrosurgical system1000 again includes a catheter or probe shaft 1002 extending to aworking end 1010 that carries an expandable dielectric structure 1022.In this embodiment, the dielectric structure 1022 includes a pluralityof interior chambers, for example first and second chambers 1024A and1024B. The expansion of the dielectric structure 1022 can be provided byskeletal support members such as interior spring-like members asdescribed above or by expansion by fluid pressure of gas inflows or acombination thereof. Each chamber is configured to carry a flexibleinterior electrode, with adjacent chambers having opposing polarityinterior electrodes, such as electrodes 1040A and 1040B indicated at (+)and (−) polarities in FIGS. 30 and 31, to allow another form a bi-polarablation. In this embodiment, the electrodes and support members cancomprise the same members. As can be seen in FIG. 30, the external wallof dielectric structure 1022 has thin wall portions 1032A and 1032B forcapacitively coupling energy to tissue, and a thicker wall portion 1042that insulates and separates the first and second chambers 1024A and1024B. The flexible electrodes 1040A and 1040B are operatively coupledto RF power source 200. The gas inflow source 150 and negative pressuresource 160 are coupled to in inflow and outflow channels communicatingwith each interior chamber, 1024A and 1024B, independently. In thetransverse sectional view of FIG. 31, the open terminations 1046 and1048 of the inflow and outflow channels can be seen in each interiorchamber, 1024A and 1024B. Thus, each chamber is provided with acirculating gas flow (indicated by arrows in FIG. 30) similar to thatdescribed in previous embodiments with respect to single chamber workingends.

FIG. 31 is a schematic sectional view of the dielectric structure 1022deployed in a targeted tissue 1050. It can be understood that the systemcan be actuated to circulate gas in chambers 1024A and 1024B which thenis converted to a plasma 240 in each chamber as described previously. Inthis embodiment and method of use, the capacitive coupling occursthrough the thin dielectric walls 1032A and 1032B in paths of currentflow indicated at 280 in FIG. 31. Whereas the previous embodimentsillustrated a single chamber containing a plasma that capacitivelycoupled current to a non-gas electrode, the embodiment of FIGS. 30 and31 depicts the use of at least two contained plasma electrodes andcapacitive coupling therebetween. It should be appreciated that thenumber of adjacent chambers carrying opposing polarity electrodes can beutilized in a thin-wall dielectric structure, for example 2 to 10 ormore, with the chambers having any suitable dimensions or orientationsrelative to one another.

Another embodiment of the invention is schematically depicted in FIGS.32-34, wherein the electrosurgical system and working end 1200 comprisesa compliant RF energy delivery surface carried at the distal end of aprobe. In FIG. 32, a catheter shaft 1204 carries the working end 1200which comprises an expandable elastomeric balloon 1205 that can beexpanded by inflation from a liquid or gas source. The exemplary balloon1205 can be carried at the working end of any flexible catheter or rigidprobe, and can be used to deliver ablative energy to tissueintraluminally or interstitially in various procedures as describedabove. In one embodiment, such a balloon 1205 can be used in a procedureto treat atrial fibrillation as depicted in FIG. 21. The embodiment ofFIG. 32 can be used with or without creating a plasma in the interior ofthe balloon 1205, and is described next using only RF energy appliedthrough electrodes of the invention.

In FIG. 32, the balloon 1205 is configured with compliant electrodesregions 1210A and 1210B that have opposing polarities and function as abi-polar electrode arrangement. The electrodes are operatively coupledto a conventional RF source 1215A and controller 1215B. The enlargedview of FIG. 32 illustrates that balloon 1205 has a wall 1220 thatcomprises an electrically conductive knit structure 1222 that isembedded in an elastic polymer indicated at 1225. The elastomer cancomprise silicone or another similar polymer. The knit structure 1222can be fabricated by a technical knitting machine, such as systemsmanufactured by Stoll America Knitting Machinery, Inc., 250 West 39thStreet, 10018 New York, N.Y. The knit structure 1222 can have yarn 1228that is non-stretchable or stretchable and the yarn can comprise aconductive metal filament, a polymer filament with a conductive coatingor polymer filament with a conductive ribbon yarn to thus impartelectrical conductivity to the structure 1222. The deformability orelasticity of the knit structure 1222 can be provides by either or boththe elastic characteristics of the yarn 1228 or the knit pattern thatpermits stretching by yarn straightening when under loading.

FIGS. 33A-33B depict one method of fabricating a stretchable electrodethat is integrated into balloon wall 1220. FIG. 33A schematicallydepicts an exemplary conductive knit structure 1222 that is dimensionedto conform to, or stretch to fit, over a core pin 1230 of a conventionalinjection mold. It should be appreciated that the core pin 1230 can beany suitable shape, and the distal end of a blunt core pin 1230 is shownfor convenience. FIG. 33B schematically depicts the core pin 1230 andknit structure 1222 disposed in a tool configured to mold a thin-wallballoon around the core pin 1230. As can be seen in FIG. 33B, theinjection of an elastomer 1225 into the tool will create a thin-wallballoon 1205 with the knit structure embedded therein. The balloon wallcan have any suitable thickness, for example from 0.001″ to 0.080″.

As can be seen in FIGS. 33A and 33B, the knit structure 1222 can bedesigned to have a three-dimensional thickness KT to substantiallyoccupy the wall thickness WT provided by the mold, or the knit thicknessKT can be less than the thickness of wall 1220. In the embodiment ofFIGS. 33A-33B, the knit structure 1222 is embedded in a surface regionof the elastomer 1225. After molding of the balloon wall as shown inFIG. 33B, the balloon 1205 can be turned inside-out as shown in FIG. 34,and portions of the surface of the knit structure 1222 will be exposedin the surface of wall 1220. More in particular, small regions 1244 ofthe yarn 1228 that are part of the 3-dimensional knit structure that apressed into contact with the core pin 1230 can remain exposed in theballoon surface, which in turn allows the conductive knit 1222 tocontact tissue and thus function as an RF electrode. The balloon can befurther dip molded or injection molded to add thickness to the side ofthe balloon wall having the exposed yarn portions 1244. Referring backto FIG. 32, it can be seen how the electrode regions 1210A and 1210Bcomprise a plurality of exposed conductive yarn portions indicated at1244.

FIG. 35 shows another form of conductive yarn 1245 from which the knitstructure 1222 of FIGS. 32-33B can be fabricated. The yarn 1245 of FIG.35 comprises a non-conductive core yarn element 1246 which can be anelastic polymer which is helically wound with an electrically conductivefilament 1248. It should be appreciated that the conductive filament1248 can comprise a woven or braided structure around the core yarnelement. In another embodiment, the yarn can comprises a positivetemperature coefficient polymer filament.

FIG. 36 depicts another embodiment 1250 of the invention wherein theworking end comprises an introducer 1252 that caries a compliant balloon1255 shaped for an endometrial ablation procedure. The balloon can bemechanically expanded by an expandable frame as is known in the art. Theballoon 1255 can be fabricated by an injection molding process asgenerally described in FIGS. 33A-33B. FIG. 36 schematically depicts theexposed conductive filament regions 1244 in an arrangement that providesbi-polar electrodes 1260A and 1260B. In another embodiment, the workingcan be configured to operate in a mono-polar manner with the exposedconductive filament regions 1244 comprising a single pole cooperatingwith a ground pad.

In a method of use to apply ablative energy to tissue, it has been foundthat the conductive knit structure can be designed and fabricated toallow a very high current-carrying capability and further to allow forcontrolling the depth of the ablation by varying the electrode exposurein the surface of wall 1220 and the distribution of exposed conductiveregions 1244 (FIG. 34.) In one aspect of the invention, the totalelectrode exposure can range between about 5% to 80% of the totalsurface area, or between about 5% and 50% of the total surface area.

In FIG. 37, an exemplary surface of a complaint wall 1220 is shown withexposed conductive regions 1244 or electrodes shown. By use of atechnical knit, the pattern and 3-dimensional characteristics of theknit can be engineered to provide the selected degree of exposure of theconductive regions 1244, and further can be engineered to provide aselected pattern of exposed conductive regions 1244, spacing betweenindividual exposed conductive regions 1244 and groups or such regions,and alignment or axes of groups of such exposed conductive regions 1244.For example, in FIG. 37, it can seen that a selected spacing SP isprovided between individual exposed conductive regions 1244 and selectedspacing SP′ is provided between a row of exposed conductive regions1244. Further, selected spacing SP is provide between groups of exposedconductive regions 1244 that may comprise opposing polarity electrodes.

Now turning to FIG. 38, a thin-wall elastomeric working end 1270 isshown that is configured for endometrial ablation similar to that ofFIG. 36. In this embodiment, it can be seen that a central portion 1275of the working end is configured with a higher density of exposedconductive regions 1244, while laterally outward regions 1276 a and 1276b have lower density of exposed conductive regions 1244. Likewise, aproximal portion of working end 1270 is configured with a lower densityof exposed conductive regions 1244. In operation in a mono-polar mode,in general, the working end portions with greater electrode exposure,such as portion 1275, will cause greater ablation depth than working endportions with lesser electrode exposure.

In another embodiment (not shown), a knit structure 1222 as in FIG. 34can be knit from a plurality of different yarns wherein each yarn has adifferent current-carrying capacity, or resistance to current flow. Inthis embodiment, the knit pattern can be adapted to provide variedenergy delivery through varied characteristics of the exposed electroderegions to control the depth ablation adjacent to the working end.

Although particular embodiments of the present invention have beendescribed above in detail, it will be understood that this descriptionis merely for purposes of illustration and the above description of theinvention is not exhaustive. Specific features of the invention areshown in some drawings and not in others, and this is for convenienceonly and any feature may be combined with another in accordance with theinvention. A number of variations and alternatives will be apparent toone having ordinary skills in the art. Such alternatives and variationsare intended to be included within the scope of the claims. Particularfeatures that are presented in dependent claims can be combined and fallwithin the scope of the invention. The invention also encompassesembodiments as if dependent claims were alternatively written in amultiple dependent claim format with reference to other independentclaims.

1. A method of applying energy to tissue comprising: providing acomplaint energy-delivery construct comprising a non-conductiveelastomer with a conductive knit embedded therein; expanding theconstruct in the interior of a patient's body to engage tissue; anddelivering RF energy to the conductive knit which thereby causes energyapplication about the construct to the engaged tissue.
 2. The method ofclaim 1 wherein conductive knit is configured for mono-polar RF energyapplication.
 3. The method of claim 1 wherein conductive knit isconfigured for bi-polar RF energy application.
 4. The method of claim 1wherein conductive knit is configured to provide varied exposure of theconductive knit in a surface of the construct.
 5. The method of claim 1wherein conductive knit provides at least two different degrees ofexposure of the conductive knit in a surface of the construct.
 6. Themethod of claim 1 wherein the construct is expanded by inflation.
 7. Themethod of claim 1 wherein the construct is expanded by an expandableframe.
 8. A system for applying RF energy to tissue, comprising: a probehaving a working end comprising a compliant RF energy-delivery surface;the RF energy-delivery surface comprising a thin-wall elastomer with anelectrically conductive knit component therein; and an RF source coupledto the conductive knit component.
 9. The system of claim 8 wherein theRF energy-delivery surface has a first non-expanded shape and isexpandable to a second expanded shape.
 10. The system of claim 8 whereinthe RF energy-delivery surface has an interior fluid-tight chamber. 11.The system of claim 8 wherein the RF energy-delivery surface is moveablefrom the first non-expanded shape to the second expanded shape byinflation.
 12. The system of claim 8 wherein the RF energy-deliverysurface is moveable from the first non-expanded shape to the secondexpanded shape by an expandable frame.
 13. The system of claim 8 whereinthe knit component has spaced apart electrically conductive portionseach coupled to opposing poles of the RF source.
 14. The system of claim8 wherein the knit component has an exposure in the surface rangingbetween 5% and 80%.
 15. The system of claim 8 wherein the knit componenthas an exposure in the surface ranging between 5% and 50%.
 16. Themethod of claim 1 wherein knit component is fabricated to provides atleast two different degrees of exposure in the surface.
 17. The methodof claim 1 wherein knit component is fabricated to provides variedspacing between different regions of the knit portions exposed in thesurface.
 18. The method of claim 1 wherein knit component is fabricatedof at least two different yarns having different electrical properties.19. The method of claim 1 wherein knit component is fabricated of atleast two different yarns having different cross-sections.
 20. Themethod of claim 1 wherein knit component is fabricated of at least twodifferent yarns having different resistance to current flow.
 21. Amethod of fabricating a complaint construct for applying RF energy totissue, comprising: knitting a knit structure using yarn that carries anelectrically conductive component; positioning the knit structure withinthe cavity of an injection mold configured to mold a thin wallstructure; and injecting an elastomer into the mold, wherein the knitstructure is at least partly embedded in the elastomer thereby providinga compliant construct carrying a conductive yarn electrode.
 22. Themethod of claim 21 wherein the knit structure comprises stretchableyarn.
 23. The method of claim 21 wherein the knit structure isconfigured to be partly embedded in the elastomer and partly exposed.24. The method of claim 21 wherein the positioning step places the knitstructure over a core pin of the mold.